This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A338828 #13 Nov 12 2020 11:50:22 %S A338828 0,0,0,4,0,4,8,4,0,10,0,10,10,0,10,10,0,10,20,10,0,20,10,0,20,10,0,28, %T A338828 0,28,40,12,40,52,24,52,40,12,40,28,0,28,40,12,40,52,24,52,40,12,40, %U A338828 28,0,28,56,28,0,68,40,12,80,52,24,68,40,12,56,28,0,68 %N A338828 For any number with ternary representation (t(1), t(2), ..., t(k)), the ternary representation of a(n) is (abs(t(1)-t(k)), abs(t(2)-t(k-1)), ..., abs(t(k)-t(1))). %C A338828 Leading zeros are ignored. %H A338828 Rémy Sigrist, <a href="/A338828/b338828.txt">Table of n, a(n) for n = 0..6561</a> %F A338828 a(n) = 0 iff n is a palindrome in base 3 (A014190). %p A338828 a:= n-> (l-> (h-> add(h[j]*3^(j-1), j=1..nops(h)))([seq( %p A338828 abs(l[i]-l[-i]), i=1..nops(l))]))(convert(n, base, 3)): %p A338828 seq(a(n), n=0..70); # _Alois P. Heinz_, Nov 12 2020 %o A338828 (PARI) a(n, base=3) = my (d=digits(n, base)); fromdigits(abs(d-Vecrev(d)), base) %Y A338828 Cf. A014190, A175919 (binary analog), A338827 (decimal analog). %K A338828 nonn,base,look %O A338828 0,4 %A A338828 _Rémy Sigrist_, Nov 11 2020